feedgnuplot/guide/guide.org

• Guide

Guide

This is an overview of the capabilities of feedgnuplot and a set of example recipes. The documentation provides a complete reference. The capabilities of gnuplot itself are demonstrated at its demo page.

First, a trivial plot: let's plot a sinusoid

seq 100 | \
    perl -nE 'say sin($_/5.)' | \
    feedgnuplot

This was a trivial plot, and was trivially-easy to make: we gave the tool one column of data with no specific instructions, and we got a plot.

Here each point we plotted was 2-dimensional (has an x value an a y value), but we passed in only one number for each point. This is what is expected without --domain, so feedgnuplot filled in sequential integers (0, 1, 2, …) for the x coordinate. Without --domain and without --dataid, each line of input is interpreted as y0 y1 y2.... So we can plot a sin and a cos together:

seq 100 | \
    perl -nE '$th = $_/100.*2.*3.14159; $s=sin($th); $c=cos($th); say "$c $s"' | \
    feedgnuplot

Note that, the lines may have different numbers of points. To plot the cos from every line, but a sin from every 5th line:

seq 100 | \
    perl -nE '$th = $_/100.*2.*3.14159; $s=sin($th); $c=cos($th);
              if($.%5) { say "$c"; } else { say "$c $s"; }' | \
    feedgnuplot

If we pass in two columns and --domain, feedgnuplot will use one for the x, and the other for the y. With --domain and without --dataid, each line of input is interpreted as x y0 y1 y2.... Let's plot sin(theta) vs. cos(theta), i.e. a circle:

seq 100 | \
    perl -nE '$th = $_/100.*2.*3.14159; $s=sin($th); $c=cos($th); say "$c $s"' | \
    feedgnuplot --domain

Hmmm. We asked for a circle, but this looks more like an ellipse. Why? Because gnuplot is autoscaling the x and y axes independently to fill the plot window. We can scale the axes together by passing --square, and we get a circle:

seq 100 | \
    perl -nE '$th = $_/100.*2.*3.14159; $s=sin($th); $c=cos($th); say "$c $s"' | \
    feedgnuplot --domain --square

Again, we can have multiple y in each line, and each line may have a different number of y. Let's plot a circle and an ellipse, sampled more coarsely:

seq 100 | \
    perl -nE '$th = $_/100.*2.*3.14159; $s=sin($th); $c=cos($th);
              if($.%5) { say "$c $s"; } else { $s2 = $s/2; say "$c $s $s2"; }' | \
    feedgnuplot --domain --square